rEFIt is perfect. Causes no issues whatsoever and also supports booting with usb drives as well which is something that macs have lacked for the longest time. Also if you decide to uninstall it all you have to do is erase the rEFIt folder that it installs on the OSX partition and you are done. Reboot and its like it was never there. Another neat thing I found out the other day about rEFIt was that if you want to install windows XP on a separate USB hard disk, you can as well. This is all you need to do:
1. Create two partitions on your USB hard drive with disk utility. A small 20mb HFS+ partition and another ms-dos one where you will install windows xp.
2. Download rEFIt and copy the efi folder in the mpkg to the 20mb HFS+ partition on the usb drive and run the .sh file to initialize the efi bootloader on the drive.
3. Have your usb drive plugged in and reboot the mac, hold c while booting to boot to windows xp cd and install xp on the other ms-dos partition on the usb drive.
4. Now when you turn on the mac hold down option and you will see the your osx partition and the refit 20mb partition on the usb drive, click on the refit one and you will then get the graphical interface that shows your OSX partition and your windows xp partition on the USB drive. Choose the windows xp partition to boot and you are set. Install bootcamp drivers and enjoy.
I have also managed to install Debian 4.0 on a 2gb usb memory stick using this method so it works for any OS you want.
Edit: Also if you want the windows that is installed the usb hard drive to work on another PC and not just the mac you have to change some files on the install cd. Follow this guide: